Left-Turn-On-Red Traffic Scheme in Singapore

Institute of Transportation Engineers. ITE Journal, Nov 2004 by Wong, Y D, Ho, J S, Foo, H Y T

LEFT-TURN-ON-RED (LTOR), THE EQUIVALENT OF NORTH AMERICA'S UBIQUITOUS RIGHT-TURN-ON-RED, WAS INTRODUCED IN SINGAPORE IN 1997. PRESENTLY, MORE THAN 40 LTOR TRAFFIC CONTROLS ARE IN OPERATION IN SINGAPORE. AN EVALUATION STUDY REVEALED A SUBSTANTIAL REDUCTION IN PEAK-HOUR VEHICLE STOPPED DELAY AS A RESULT OF LTOR OPERATION. OVERALL, THERE WAS A SMALL INCREASE IN ACCIDENT OCCURRENCES.

INTRODUCTION

In Singapore, traffic signals are the predominant type of traffic control at major intersections. Conflicting movements are segregated by means of phased signal indications. More than 1,100 traffic intersections are under signalized operation.

Where left-turning volumes are high and land space permits, channelized leftturn slip roads are constructed at signalized intersections in Singapore. This allows vehicles to turn left and merge with the cross-flow under a "give way" control. It should be noted that Singapore operates a right-hand drive system similar to that in the United Kingdom.

In April 1997, the Singapore Land Transport Authority launched the left-turn-on-red (LTOR) scheme, a traffic management practice that is equivalent to right-turn-on-red (RTOR) in North America. LTOR traffic control permits motorists to turn left on a red traffic signal indication after stopping and giving way to conflicting vehicles and crossing pedestrians.1

LTOR in Singapore began with two intersections. The scheme was progressively expanded to more than 50 intersections within a year, and more intersections were added in later years. LTOR was removed at certain implemented sites that subsequently experienced unfavorable conditions. Presently, more than 40 LTOR traffic controls are in operation.

This feature describes the implementation of the LTOR traffic scheme in Singapore. A brief review concerning the application of and issues surrounding RTOR/LTOR is presented. In addition, the results of an evaluation study on the vehicle stopped delay and accident experience at LTOR intersections are reported.

It should be noted that, in recent years, turning on red in the other direction (LTOR in the United States) has been permitted by some U.S. jurisdictions, although it has been applied strictly at the intersection of two one-way streets. Except for the distinction made here, this scheme will not be covered any further. In this feature, RTOR (in the United States), LTOR (in Singapore) and TOR are used interchangeably and refer to the same scheme.

TOR TRAFFIC CONTROL

The application of TOR traffic control originated in the United States, and most associated research studies have been based on the American experience with RTOR. The RTOR scheme was introduced in New York City in 1924 but was discontinued in 1937. Also in 1937, RTOR with an authorizing sign was permitted in California. In 1947, RTOR was changed to a generally permissive system that allowed motorists to turn right on red unless a sign prohibited such turns.

RTOR spread gradually to other states over the next 30 years.2 It was widely adopted during the 1970s when the federal government linked RTOR implementation to eligibility for federal funding as part of an effort to put all possible energy efficiency measures into effect.3 By 1977, RTOR under the generally permissive rule was effective nationwide at a high percentage of signalized intersections.4

The application of RTOR has been extended further in some jurisdictions to allow part-time RTOR during periods when there are relatively few conflicts.5,6 The TOR scheme is touted as providing a number of benefits, including reduced delays (time savings); reduced pollution at intersections and less energy consumption (energy conservation); and small increases in intersection capacity and level of service, in some cases.

The implementation of RTOR in the early years, especially under the generally permissive rule, brought a fair amount of controversy. Those in favor of RTOR cited the benefits of the scheme; opponents claimed that RTOR traffic control contributed to an increase in vehiclepedestrian and vehicle-vehicle accidents. The underlying non-uniformity in RTOR formats also created a high accident potential for interstate drivers.

These concerns led to a number of studies on RTOR (particularly concerning its impact on safety) and to the development of guidelines for RTOR applications and/or prohibitions.7-10 A fairly recent report by the National Highway Traffic Safety Administration to the U.S. Congress concluded that "There are a relatively small number of deaths and injuries each year caused by RTOR crashes. These represent a very small percentage of all crashes, deaths and injuries."11

It appears that RTOR has not resulted in the deterioration of safety in any significant way, but it is fair to say that accident risk, although small, remains largely unpredictable.

THE SINGAPORE LTOR SCHEME

The LTOR scheme in Singapore is functionally the same as the RTOR system in the United States, but the qualifying conditions are more stringent. The typical layout and associated signage at a LTOR intersection are depicted in Figure 1. Candidate intersections are chosen carefully and possess the following characteristics: